1. Field of the Invention
The present invention relates to the preparation of a colloidal dispersion of a metallic cation compound in an organic medium, and, more especially, to the preparation of an organic colloidal dispersion of a compound of a metallic cation which is acidic in character, hereinafter referred to as the cation M.sup.n+, wherein n.sup.+ symbolizes the degree or state of oxidation of the metal and which typically is equal to +3 or +4.
By a "compound of a metallic cation" as utilized herein, there is intended a compound based essentially on the metallic hydroxide thereof and an organic acid.
By a "metallic cation which is acidic in character", or acidic metallic cation, there is intended a cation, the metallic hydroxide of which precipitates at low values of pH, preferably at a pH of less than 4.
Exemplary of such acid cations, representative are the cations of cerium, iron, titanium, zirconium and tin.
In a preferred embodiment of this invention, featured is the preparation of colloidal dispersions of a compound of cerium (IV) and/or a compound of iron (III), in an organic medium.
2. Description of the Prior Art
It is known to this art, from published French Application No. 2,359,192, that certain organic salts of cerium exist which are soluble in solvents and which are characterized in that they have a ratio r between the number of acid equivalents and the number of cerium atoms of from 0.2 to 1; the number of acid equivalents represents the number of acid molecules if the acid used is monofunctional, and it is necessary to double and triple this number in the case of diacids or triacids and, more generally, multiply it by the number of acid functions in the case of a polyacid. The cerium compounds proposed in this manner require a much smaller amount of the acid than the amount theretofore used to obtain the same effect. It is also possible to obtain solutions with higher metal concentrations of up to 500 g/l; the solutions obtained remain fluid and may be manipulated without difficulty while remaining perfectly soluble in hydrocarbon media.
The organic acid may be RCOOH, RSO.sub.3 H, ROSO.sub.3 H, ROPO.sub.3 H.sub.2 or (RO).sub.2 PO.sub.2 H, with R being a hydrocarbon radical having at least 7 carbon atoms. The organic radical may be a linear or branched chin aliphatic radical or a cyclo-aliphatic radical optionally substituted by an alkyl radical or by an aromatic radical itself optionally substituted by an alkyl radical. The cerium salts of these organic acids may further contain at least one other rare earth metal, e.g., up to 25% of the total content of rare earth metals, including the cerium. It is possible to obtain compositions in the form of solutions in an organic solvent containing more than 200 g cerium per liter of the composition.
The process for the preparation of these cerium salts of an organic acid, or mixtures thereof, consists of reacting, in an organic or a hydroorganic medium, the organic acid and freshly prepared cerium hydroxide Ce(OH).sub.3, in a manner such that the product cerium salts of the organic acid have a ratio r of from 0.2 to 1. The reaction is preferably carried out under heating and the organic medium is preferably a hydrocarbon. After several hours, a part of the water formed during the reaction decants spontaneously. After the reaction, it is possible to assist the separation of the water formed from the reaction medium by adding thereto a third solvent, such as a glycol, an alcohol or an alkyl glycol. The concentration of the solution obtained in this manner is adjusted by adding an appropriate hydrocarbon.
In the examples in this application, the cerium hydroxide Ce(OH).sub.3 is obtained by the precipitation of cerium with ammonia. The precipitate is washed in water until the nitrate ion disappears, and it is then filtered until the nitrate ion disappears, and it is then filtered until it contains less than 15% water. The cerium hydroxide is reacted at 80.degree. C. with 130 g commercial oleic acid in white spirit. After four hours, glycol is added, the separated water eliminated and, subsequently, butyl-glycol added, followed by white spirit to form the final solution.
A process for the preparation of colloidal dispersions of ceric dioxide in inert organic liquids has also been proposed to this art, in published European Application No. 0,097,563, which process consists of:
[1] heating to between 60.degree. C. and 200.degree. C. PA1 [2] then eliminating the water, methanol, the acetic acid evolved during heating and separating all of the undissolved solid particles. PA1 (i) The necessity for the preparation of fresh solid ferric hydroxide when preparing an organic salt from the solid hydroxide; and PA1 (ii) The necessity for a rigorous control of the process parameters (agitation mixing conditions) in the case of the preparation of the organic salt using a ferric hydroxide prepared in situ. PA1 (i) contacting: PA1 (ii) subsequently separating the aqueous phase and the organic phase. PA1 (i) the proportion of the metal M in the colloidal form should be as high as possible, and preferably greater than or equal to 95%; PA1 (ii) the concentration of the cation M.sup.n+ in the aqueous sol must be adequate and preferably ranges form 0.1 to 3 moles/liter; and PA1 (iii) the aqueous sol must have good thermal stability and must not flocculate at the temperature of the reaction, which is higher than 60.degree. C. and most frequently ranging from 80.degree. to 100.degree. C. PA1 n1 represents the number of moles of Ce (IV) values present in the final colloidal dispersion; PA1 n2 represents the number of moles of OH.sup.- necessary to neutralize the acidity introduced via the aqueous solution of the cerium (IV) salt; and PA1 n3 represents the total number of moles of OH.sup.- introduced by the addition of the base. PA1 with r=4, the cerium (IV) precipitates in a gelatinous form; PA1 with r=0, the cerium (IV) is in the ionic form; and PA1 with o&lt;r&lt;4.0, the cerium (IV) is in the ionic and/or colloidal form. PA1 [OH.sup.- ] is the concentration in moles/liter of the basic solution: PA1 [Ce (IV)].sub.f is the concentration in Ce (IV) in moles/liter of the product colloidal dispersion; PA1 [Ce (IV)].sub.i is the concentration in Ce (IV) in moles/liter of the aqueous solution of the cerium (IV) salt; and PA1 n.sub.1 and n.sub.2 are determined by conventional analysis of the aqueous solution of the cerium (IV) salt; PA1 15 to 85% of a cerium (IV) compound expressed as the weight of cerium with respect to the total weight of the metals, and PA1 15 to 85% of an iron (III) compound expressed as the weight of iron with respect to the total weight of the metals.
(a) ceric dioxide containing ammonium nitrate in an amount representing from 3% to 14% by weight of the ceric dioxide and a member selected from the group consisting of water, methanol, acetic acid and mixtures thereof in an amount of at least 10 g per mole of CeO.sup.2. PA2 (b) an organic acid having approximately 10 to 40 carbon atoms, in particular oleic acid. PA2 (c) an organic liquid selected from the group consisting of aliphatic, cycloaliphatic and aromatic hydrocarbons, aliphatic and cycloaliphatic ethers or ketones; and PA2 (a) an aqueous phase which comprises at least one colloidal dispersion of at least one compound of the said M.sup.n+ cation in an aqueous medium supersaturated in OH.sup.- ions, obtained by the reaction of an M.sup.n+ cation with a base, PA2 (b) an organic phase comprising an organic acid and a liquid organic medium or solvent; and PA2 n.sub.1 by potentiometric titration with the aid of a solution of ferrous salt, and PA2 n.sub.2 by acid/basic titration after complexing the cerium with the aid of oxalate ions.
A colloidal dispersion of ceric dioxide in an organic medium is obtained, with the ceric dioxide being present in the form of a complex resulting from the physical combination of CeO.sub.2 with the organic acid.
It follows from this analysis of the prior art that the processes enabling the preparation of organic sols of ceric dioxide use as their beginning starting material hydrated ceric dioxide, which is most frequently produced by the oxidation and precipitation with a base of a cerium (III) salt, followed by the separation of the resulting precipitate.